Hi-NICALON(TM) Type S fiber tow surface desizing and decarburization via heat treatment

HI-NICALONTM Type S SiC fibers are the current state of the art commercially-available silicon carbide ceramic fibers with minimal oxygen content, high strength and creep resistance. While their stoichiometry is near 1:1 C: Si, there is still excess carbon present on the fiber surface, adjacent to the fiber surface, and throughout the fiber, from synthesis, and they are shipped under a sizing of polyvinyl alcohol to prevent damage during handling. For incorporation into a CMC, removal of both the excess carbon and sizing while maintaining the fiber strength is desired. This manuscript aims to perform both surface decarburization and desizing of HI-NICALONTM Type S SiC fiber tows while maintaining strength. A mechanism of the two processes is proposed through the use of TPD-MS and TGA-MS. Based on those thermal results, hydrogen and argon environments at elevated temperatures are used to desize and decarburize these fiber tows. SEM, Auger, and SIMS are used to study the fiber tow surfaces to determine the degree to which desizing and decarburization occurred. Tensile testing of treated fiber tows was performed to determine strength reduction caused by each treatment. A combination of hydrogen and argon at 1000 degrees C demonstrated the greatest desizing and decarburization, and resulted in little to no strength reduction or oxidation of the SiC fibers.